https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106570
Bug ID: 106570 Summary: DCE sometimes fails with depending if statements Product: gcc Version: 12.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: tmayerl at student dot ethz.ch Target Milestone: --- Sometimes, DCE fails when multiple if statements are used. For example, GCC detects that the following if statements always evaluate to false and thus removes the dead code: #include <stdio.h> #include <stdbool.h> void DCEMarker0_(); void f(bool s, bool c) { if (!c == !s) { if (s && !c) { DCEMarker0_(); } } } In the next snippet, the if statements are used to set a variable. This variable is then used in the next if statement. However, GCC now fails to detect and eliminate the dead code: #include <stdio.h> #include <stdbool.h> void DCEMarker0_(); void f(bool s, bool c) { int intermediate_result = 0; if (!c == !s) { if (s && !c) { intermediate_result = 1; } } if (((!c == !s) && (s && !c)) || intermediate_result) { DCEMarker0_(); } } This is actually a regression: It works fine until GCC 11.3. This can also be seen via the following Compiler Explorer link: https://godbolt.org/z/n9dKMfqsd